1. Field of the Invention
This invention relates to a mold closing unit for use in an injection molding machine for processing synthetic materials, comprising an electro-mechanical driving unit jointedly connected with a movable mold carrier and a supporting element by a toggle mechanism and arranged transversally with respect to a closing direction. The electro-mechanical driving unit is held freely movable by the toggle mechanism, which is adapted to move the movable mold carrier in and out of a closed position with the stationary mold carrier in the closing direction and comprises a driving element for driving the toggle mechanism.
2. Description of the Prior Art
From German Published Patent Application 42 30 348 a machine of this kind is known, in which a supporting element and a mold carrying plate are jointedly connected with a machine base of cast iron, which deviates the forces occuring during the closing and the injection process. The movable mold carrier and the supporting element are jointedly connected by a toggle mechanism, at which a driving device is freely suspended at link points of toggle levers, whereby evasive movements of the movable mold carrier are avoided. The principle followed is to form the machine base so rigidly that it is only minimally deformed under the occuring forces and additionally, to keep away the remaining deformations from the mold by the jointed bearing. Mechanical and/or electrical drives are suggested as driving units, however, hydraulic and pneumatic drives are prefered with regard to their space requirement.
Those linear drives, which transmit a rotational movement, preferably of an electro-mechanical drive, to a linearly moving element, are provided with a ball rolling spindle as for example disclosed in European Patent 271 588 and with a double toothed rack as known from European Published Patent Application 427 438. However, in all these cases the linear drive is used as drive actuating directly in closing direction, which again acts directly upon the movable mold carrier, so that the space required for the linear drive plays only a secondary part. In such an arrangement problems concerning the reproduceability of of the closing force crop up, due to the difficultly in controlling the backlash of threads.
According to European Patent 164 419 a ball rolling spindle can also be used for actuating a toggle. Here only low current is necessary in order to keep the toggle in its extended position. However, the linear drive is mounted in a separate place at the machine base, so that additional space is required for the drive, but since in this arrangement the spindle and the motor are supported in a way that permits rotational movements only, this is a burden.